ALSA: firewire-motu: fix unreleased lock warning in hwdep device

Smatch static analysis tool detects that acquired lock is not released
in hwdep device when condition branch is passed due to no event. It is
unlikely to occur, while fulfilling is preferable for better coding.
Reported-by: Dan Carpenter <error27@gmail.com>
Fixes: 634ec0b2 ("ALSA: firewire-motu: notify event for parameter change in register DSP model")
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Link: https://lore.kernel.org/r/20230130141540.102854-1-o-takashi@sakamocchi.jpSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/firewire/motu/motu-hwdep.c

@@ -87,6 +87,10 @@ static long hwdep_read(struct snd_hwdep *hwdep, char __user *buf, long count,
 			return -EFAULT;
 
 		count = consumed;
+	} else {
+		spin_unlock_irq(&motu->lock);
+
+		count = 0;
 	}
 
 	return count;